Traditional cast-in-place concrete retaining walls are fast becoming untraditional. They cost too much and take too long to build. Newer concrete wall systems have replaced them in many instances. The newer systems are less costly and quicker to build. Many require less excavation and cause less traffic disruption.

TRADITIONAL CAST-IN-PLACE WALLS

There are three types of cast-in-place walls: gravity, cantilever, and counterfort. Each of these walls is constructed with a base slab or footing. The gravity wall relies mostly on its own weight to resist earth pressure. The wall portion (or stem) of a cantilever wall cantilevers from the base slab. The wall is thinner than a gravity wall, but it's reinforced along the back face and in the base where loading induces tensile stress. In counterfort walls, the base slab and wall span between vertical triangular braces. These concrete braces are called counterforts if they're on the earth side of the wall. If they're exposed at the front, they're called buttresses.

MECHANICALLY STABILIZED EARTH (MSE) WALLS

The earth backfill behind a concrete wall facing can be made to support itself by layering reinforcement within the backfill. The soil itself becomes a self-supporting structure. At least four proprietary MSE systems are available in the United States. Each system has three main parts: the concrete facing, backfill, and reinforcement.

GROUND-ANCHORED WALLS

Ground-anchored walls are thin concrete retaining walls that are permanently anchored to firm ground by grouted ties. The bar or strand ties are called permanent ground anchors or tiebacks. They generally are inserted into holes that are drilled or driven into the existing soil or rock behind the wall.

SOIL NAILING

Soil-nailed retaining walls are designed like MSE walls but constructed like ground-anchored walls. Like MSE, nailed soil acts as one coherent gravity mass. Long steel rebars are inserted in the ground at close enough spacing to make the soil more self-supporting.

PRECAST PANELS ANCHORED BY PRECAST DEADMEN

Although this system is constructed much like a MSE wall, it acts more like a grouted ground-anchored wall. Epoxy-coated steel tendons connect precast concrete face panels to precast concrete deadmen buried in the backfill. The deadmen resist the lateral earth loads that press against the concrete facing.